Try picture cards. When you change his diaper show the card of either pee or poop so he begins to learn the card and threw when he needs to go he can show you the card to indicate him needing to. Hope that helps

Do you do any signing with him? There is an app called My Smart Hands, it has a lot of simple signs - perhaps the sign for potty would be enough!

I read the book Oh Crap! Potty Training before training my lo, and although it isn't perfect, one of the things it talks about is not expecting your lo to tell you when they need to go to the potty right away. It takes awhile to get to that point - it's really up to the adult to make sure they have lots of opportunities to go. So I think you can still do it, it just might take longer for him to tell you he has to go. Lots of praise and rewards are the way to go! Best of luck!

My son is also nonverbal, he has been potty trained since 18 months (while awake - I won't even attempt nighttime until he talks and naps are just as tricky). I also started getting him used to the potty etc around 8 months. He holds his wee wee to pee and his tushy to poop. If he has to go he walks to me or my hubby and does that, sometimes he will even start running to the potty after signaling that in front of us. It will take a while to potty train a nonverbal toddler - however I recommend trying the sign language for it (my son refuses any type of sign language) to see if it's effective for you. Otherwise try maybe doing the signals my son does? We did m&m's (1 for pee and 2 for poop) to train him, did stickers for poop too for it to be extra special. All those helped a ton. Once he was fully awake trained we would have occasional accidents but he's wonderful now. Sometimes a few hours will go by where he doesn't signal and honestly - we just take him because we know he needs a break to go even if he doesn't signal to us. Good luck!